Radio transmitter



Jan. 21, 1941.

H. J. H. WASSELL RADIO TRANSMITTER Filed June 22, 1959 POTENTIAL sou/ac:

T0 ADD/T10 AF BIAS saunas 7 BIAS SOURCE RFC RFC =L 1 40 a 1 RFC i 30 RFC =1 RFC RFC AMPLIFIERS AND DOUBLERS HAROLD JOSEPH H \NVENTOR #ggs WASS ELL ATZTO R N EY Patented Jan. 21, 1941 V UNITED STATES PATENT OFFICE RADIO TRANSMITTER Harold Joseph Hughes Wassell, Chelmsford, England, assignor to Radio Corporation of America, a corporation of Delaware Application June 22, 1939, Serial No. 280,469

r In Great Britain July 2, 1938 4 Claims. 178--66) This invention relates to radio and like transtube, for example a triode 2, the cathode 3 of mitters and, more particularly, to multi-tube telwhich is connected through a resistance 4 to egraph transmitters of the kind in which keying the negative terminal oi. said source, which negbetween mark" and "space" is effected by conative terminal may be earthed. Any convenient 6 trolling the potentials upon the screen grids of keying means for changing the condition of the 5 a plurality of tubes 01 the screen grid type, c. g., keying tube from the conductive to the nonpentodes, incorporated in said transmitter. conductive may be provided. For example, the

It is a usual requirement in transmitters gengrid cathode space between 5 and 3 of the keying erally that the load upon the power source from tube 2 may be shunted by a key 6 (or the con- 10 which the tubes are operated, shall not vary extacts of a keying relay) and also shunted by a 10 cessively between mark and space and, with source of potential I in series with a resistance this requirement in mind, it is desirable, there- 8, so that in the mark condition, that is with lore, to arrange that the final keyed tube of the the key closed, the keying tube 2 is conductive transmitter shall take maximum dead loss when and current will flow through the resistance 4- the other keyedtubes are in the cut-off condition. Taps 9, l0, H, which may be adjustable, are 15 The main object of the present invention is to made upon the resistance 4 and are connected provide an improved transmitter of the kind each to one or another of the screen grids of referred to, wherein keying is effected in a very the plurality of screen grid type tubes 32, 40, sirnpleand efflcient manner, and wherein the etc" except the last tube II to be subjected to to above requirement is satisfi d, keying in the transmitter- These taps are not According to this invention a transmitter of connected to the last screen grid tube l2. The the kind referred to comprises a main source of positive te o t e main Sou ce of potenpotential; :3. keying tube having its anode-cathode tial is also connected to the anodes of the said space in series with an impedance adapted to screen grid type tubes to supply anode potential as pass direct current, the series combination being thereto. The final screen grid type tube 12 to be connected across said source of potential; keykeyed; this tube, like the other screen grid type ing means for changing the condition of said-keytubes, may be a pentode, has its screen grid I3 lng tube from the conductive to the nonconconnected to the positive terminal of the main ductive state and vice versa; connections besource of potential through a resistance 14 and tween taps upon said impedance, and the screen its control grid l5 connected through a series 30 grids of certain of the screen grid type tubes to circuit consisting of a choke 16, a resistance, or be keyed; and a connection including a source other high frequency decoupling means IT, and of bias potential between a further tap on said a ias source l8. to a further tap w h m y impedance and a grid of the last of the tubes to be adjust n r h ear hed end of the cathb key d, id-f th r tap a d aid bias our ode leg resistance 4. The screen grid I3 of the 35 being so chosen that when the keying tube is in final keyed tube i2 is connected to earth throu h the conductive condition, the potential from said shy-P condenser 20 and e Junction point further tap substantially balances in opposition of the choke IS with the resistance I1 is also the potential from said bias source whereas when connected to earth through a Y-D den r said keying tube is in the non-conductive condi- 2L The s ppr s r id 22 is ear hed or con- 40 tion said bias source alone is effective and causes nected to the cathode 23. the final keyed tub to t ke th ui d i- The operation of the whole system is as folmum dead loss current. lows:

The final keyed tu e is preferably not subwhen the keying tube 2 is conductive current 5 jected to screen grid keying, the grid upon hich flows through the cathode leg impedance 4 and keying is exercised being the control grid. potentials are applied to the screen grids of the Preferably the main source or potential is used screen grid t p tubes. except tube to Cause also for supplying anode potentials to one or them to be conductive. At the same time the more of the keyed tubes and for applying screen potential from the tap l9 opposes and cancels 59 grid potential to the final keyed tube. out the potential from the bias source It and, 5

The invention is illustrated in the accompanytherefore, the final keyed tube i2 takes current ing drawing which shows diagrammatically a. as determined by the remaining operating popreferred embodiment. Referring to the drawtentials thereon. This is the state of affairs for ing, a main source I of potential has its positive mark." At space the keying tube 2 ceases terminal connected to the anode of a keying to be conductive, current ceases to flow through the cathode leg resistance 4, the potentials on the various taps thereon disappear, all the screen grid type tubes (except the last) become nonconductive and the last tube l2 takes the predetermined maximum dead loss current as determined by its operating potentials including the bias applied by the source It! in its control grid circuit.

The resistance I! in the control grid circuit of the final keyed tube l2, though preferred, is not essential. If it is provided, however, it should be substantially larger than the resistive value of the portion of the cathode leg resistance 4 between the tap l9 and earth.

The particulars of the radio-frequency circuits of the tubes keyed is of general interest here and may be as shown. Wave energy from source 30 is amplified, when the key 6 is on marking, in stages 32, 40 and I2, which are coupled by circuits 36 and 50. The keyed wave energy is set up in tank circuit 80 for any use- For example, it may be supplied from to antenna and radiated. Other types of radio-frequency circuits may be used- What I claim is:

1. A transmitter of the kind referred to comprising a main source of direct current potential, an impedance, a keying tube having an anode andcathode and having its anode to cathode impedance in series with said impedance which is adapted to pass direct current, means connecting the series combination across said source of potential, keying means for changing the condition of said keying tube from the conductive condition to the non-conductive condition and vice versa, a plurality of tubes of the screen grid type to be keyed, connections between taps upon said impedance and the screen grids of a plurality of said tubes to be keyed, and a connection including a source of bias potential between an additional tap on said impedance and an electrode of the last of the tubes to be keyed, said further tap and said bias source being so chosen that when the keying tube is in the conductive condition, the potential from said further tap substantially balances in opposition the potentlal from said bias source whereas when said keying tube is in the non-conductive condition said bias source alone is eflective/nd causes the said last keyed tube to take th equired maximum dead loss current.

2. A transmitter as claimed in claim 1 wherein said electrode connected to said additional tap is the control grid of said last keyed tube and the latter is keyed on its control grid.

3. A transmitter as recited in claim 1 wherein said electrode connected to said additional tap is the control grid of said last tube and the latter is keyed on its control grid and wherein the anodes of all of said tubes of the screen grid type, and the screen grid of said last keyed tube are connected to said main source of direct current.

4. In a telegraphy system a plurality of relay.

tubes each having an anode, a cathode and a control electrode, circuit means connecting said tubes in cascade and with a source of wave energy to be keyed, a direct current impedance, a source of direct current potential, a keying tube having its impedance connected in series with said direct current impedance and said source of direct-current potential, means for varying the impedance of said keying tube to thereby vary the potential drop through said direct-current impedance, a connection between a point on said direct-current impedance and the control electrode in at least one of said relay tubes to control the conductivity of said relay tube as said keying tube impedance is varied, a connection between said direct-current impedance and the control electrode in another of said relay tubes. and a source of direct current in said last named connection of a polarity opposed to the polarity of the potential supplied by said direct-current impedance to said last named connection.

HAROLD JOSEPH HUGHES WASSELL. 

